Vegetable IPM Update 9/09/20

Sweet Corn

European corn borer (ECB) adults continue to be very low, and no map will appear in this edition.

Fall armyworm (FAW) larval infestations are at fairly low levels.  Infestations generally are in the single digits to below 20%, and with few plantings in the whorl stage at this point in the season, FAW shouldn’t become a widespread economic problem.  However, growers should be alert to the possibility of infestations on the last of their late plantings.   Injury from newly hatched larvae shows up as “window panes” or areas where leaf tissue has been eaten down the the lower epidermis. This injury leads down into the whorl.  As larvae gain size, they begin to consume leaf tissue in its’ entirety, creating ragged holes and lots of droppings.  FAW can be tough to manage because it is resistant to synthetic pyrethroid insecticides (IRAC 3A) and because larvae are often covered by their own droppings, making contact with the insecticide more difficult.  Treat when 12% or more plants exhibit FAW injury alone, or in combination with ECB injury.

Corn earworm (CEW) moth captures have decreased slightly over the past week.  This is likely due to several nights with temperatures dropping into the low 60s and even 50s F.  The decline is representative of lower adult activity, and growers should consider this pest to still be at moderately high population levels in the state.     The current population poses a significant risk to silking corn.  The reduction in CEW catch was not enough to substantially change this weeks map from last week (see map at left).  Green areas on this map representing a 3-day spray schedule.  For further information on CEW activity, see pheromone trap information below.

The highest nightly trap catches of CEW in black light traps for the week ending 9/09/20 are as follows:

A similar temperature-based reduction in CEW pheromone catch occurred this past week (see CEW pheromone map at left).  The blacklight network is indicating a 3-day silk spray schedule in the northern counties, while the pheromone network is at 4-day.  Under these conditions, it is best to adhere to the more conservative schedule in any given area.  Red areas indicate a 3 day schedule on the pheromone map, which is in agreement with the blacklight map for southern NJ.  The number of pheromone traps deployed is much lower, resulting in much broader color bands on the map.    The current population is a serious economic threat.  It is important to use effective materials to manage this pest on silking corn.  Insecticides in the IRAC 28 class (Coragen, Besiege, Exirel) and IRAC 5 (Radiant, Blackhawk, Entrust (OMRI approved)) remain among the most useful insecticides against CEW.

The highest nightly trap catches of CEW in pheromone traps for the week ending 9/09/20 are as follows:

Silking Spray Schedules*:
South – 3 days

Central – 3  days

North – 3 days

*These recommendations are based on regional catches.  Adhere to tighter spray schedules if indicated by local trap catches.  Synthetic pyrethroids alone should NOT be used for corn earworm (CEW) protection on silking corn, or for fall armyworm (FAW) management at any stage.  Control with these materials is very inconsistent.

As night temperatures moderate, and dew periods lengthen, northern corn leaf blight (NCLB) will increase in frequency and severity.  This fungal disease causes elongated gray streaks on leaves.  The lower leaf surface will develop greenish-gray sporulation.  If cooler, moist conditions persist, this disease can invade enough tissue to limit ear size.  Lesions can also develop on husks, resulting in an unsightly ear.  If these lesions are discovered in the pre-tassel stage or earlier, fungicide applications may be warranted.  Realistic control of this disease requires a combination of protectant (mancozeb, chlorothalonil) and locally systemic fungicides in FRAC groups 3,7 and 11.  For a complete list of materials, see the Sweet Corn Section of the Commercial Vegetable Production Recommendations.

Pepper weevil (PW)

Weevils continue to be an issue at several farms.  As the season winds down, they become less important.  Some farmers have wondered whether they should continue to spray for the weevils.  This decision depends on several things, 1) how bad are the weevils? A light infestation or severe? 2) how long do you want to extend the season? 3) what is the fruit set? 4) what is the market price? 5) what is the cost of control (depending upon which insecticide is used), and 6) do you have the labor?

Farmers will need to evaluate the fruit set.  If there are only large fruit that means that the weevils have caused the plants to abort all smaller fruit and it will take about another three weeks for the fruits to mature a new set for harvesting, but that will require at least two insecticidal applications to keep the adults from laying eggs and aborting fruit.  At this point in the season, less expensive insecticides may be the best option to reduce costs.

As for control materials, Florida insecticide trials indicate that Actara, Vydate, Harvanta, and Torac provide the best results, however, there is a broad range of materials including pyrethroids and neonics that can kill the adults.  The hope is to eliminate the weevil population before it becomes established in the field.  A combination of spraying, trapping, and removal of aborted fruit would help to manage this pest.

Pheromone trap catches of beet armyworm (BAW) have increased in some areas of southern NJ traps.  Scattered individual larvae continue to appear in some northern NJ cole crop fields, indicating that there is some larval population active in the state.  Growers should be alert to the potential for infestation from this pest.  Look for clusters of pepper plants with lace-like damage to foliage near growing points (see photo at upper left).  The green caterpillars will be found among these damaged leaves (see photo at lower left).  After consuming foliage, BAW can begin to damage fruit directly.  It is also important to note that BAW, like FAW, is resistant to synthetic pyrethroid insecticides.  For this reason, materials in the IRAC 5 and 28 classes should be used in response to an infestation.

The highest nightly trap catches of BAW in pheromone traps for the week ending 9/09/20 are as follows:

Pumpkins and Winter Squash

The cucurbit downy mildew (CDM) sentinel plot  at Snyder Farm in Hunterdon County, consisting of pumpkin, watermelon, cantaloupe, butternut, acorn, cucumber and kabocha squash is used to indicate the presence of cucurbit downy mildew in the region, and what crops are affected.  As of 9/08/20, there was no CDM detected on any of the other cucurbit types, and all reported infections in our region have been on cucumber, with one (now old) from Long Island reported on muskmelon.  For regional information on this important disease, see the Cucurbit Downy Mildew Forecast webpage:  http://cdm.ipmpipe.org/.  As of this Tuesday (9/08/20), New Jersey was rated at minimal risk for new infections by CDM from current regional sources.

As fruit mature, and vines begin to decline in some fields, growers may notice that white pits have formed on some fruit (see photo at left).  These may also be sunken on the fruit surface, and can have a gum-like ooze extruding from the lesions.  This is bacterial leaf spot, as it infects fruit.  Despite including copper in regular powdery mildew sprays, bacterial leaf spot infections on fruit are fairly common this year. These fruit may not hold well in storage, and growers should consider not adding them to bins in case they break down.   Fungicides and suggested rotations are found in the Pumpkin and Winter Squash section of the Commercial Vegetable Production Recommendations.  

Melon aphid (see photo at left) populations are more frequent in pumpkin and winter squash fields.  This aphid builds to heavy populations that result in the deposition of sticky droppings on the surface of fruit (see photo at right).  If melon aphids appear in more than one sample site in a 10 site sample, consider treating to minimize the appearance of droppings.  Insecticides effective at managing this pest are found in the Pumpkin and Winter Squash section of the Commercial Vegetable Production Recommendations.

Brown Marmorated Stink Bug

Brown marmorated stink bug (BMSB) activity has decreased to very low numbers in blacklight traps throughout New Jersey, and no map will appear in this edition.  This is often the case late in the summer.  Bugs become less attracted to light traps and are caught in greater numbers in pheromone traps.   While this pest has generally declined as a threat to peppers, it remains a significant threat to tree fruit.

Cole Crops

Fall plantings of cole crops are well underway at this time, and are frequently infested by imported cabbageworm (ICW) and diamondback moth (DBM) larvae.  At this time, cabbage looper (CL-photo at left) and cross striped cabbage worm (CSCW-photo at right) are also causing injury to these crops.

Check 5 consecutive plants each in 10 random locations throughout the planting.  Consider treating if caterpillars are found on 10% or more plants that are in the 0-9 true leaf stage.  From 9-leaf to the early head stage (in broccoli, cauliflower, and cabbage) infestations up to 20% may be tolerated.  Once heads begin to form, a 5% threshold should be observed to protect the marketable portion of the plant.  For leafy greens such as collards and kale, 10% plants infested is the threshold throughout.

Some populations of DBM are resistant to carbamate and synthetic pyrethroid insecticides.  The lack of DBM control with these insecticides has been noted in NJ previously.  It is important to distinguish between common cole crop pests for this reason.  DBM larvae grow to a length of approximately 0.5”, and taper toward both ends (see photo at right).  These caterpillars thrash violently when disturbed.  Newer chemistries that specifically target caterpillar pests are effective against DBM as well as all other caterpillar pests of cole crops, including beet armyworm (BAW), another species with exhibiting pyrethroid resistance.  These materials include (active ingredient – trade name (IRAC* code)):

Spinosad/Spinetoram – Entrust(OMRI)/ Radiant (5)

Chlorantraniliprole – Coragen (28)

Cyantraniliprole – Exirel (28)